Major depressive disorder (MDD) is the most common mental disorder, associated with major personal, societal, and economic costs. Unfortunately, a poor understanding of the pathophysiology of depression has impeded the development of effective treatments for many patients. To address these unmet needs, a better understanding of the neurocognitive mechanisms implicated in the onset and maintenance of depressive illness is necessary. Although a wealth of research has examined the role of trait rumination as a cognitive vulnerability for depression, comparatively little attention has been given to the ways in which rumination functions in real-time at the state level. Given that self-report trait measures can fall prey to retrospective recall biases, it is crucial to examine rumination as it occurs naturally in varied contexts to best understand the mechanisms through which this cognitive vulnerability may confer risk for depression. This proposal seeks to employ ecological momentary assessment (EMA) techniques to better understand the role of ruminative thought in response to stressful life events as a vulnerability for the development of depressive symptoms. It is hypothesized that rumination may increase encoding of negative life events, improve subsequent recall of this information, and therefore contribute to further depressed affect. A secondary aim of this research is to examine self-focused ruminative thought in the absence of proximal stressors as an additional predictor of depression. First onset of MDD often occurs during early adulthood and especially during college, a period of novel and increased stressors. Therefore, the proposed study aims to investigate the ways in which state-level rumination, both in the presence and absence of proximal life stress, may contribute to the development of depressive symptoms among undergraduates at an age of risk for depression. Participants will complete a battery of self-report questionnaires at the Day 1 lab visit, includin measures of trait-level rumination and depressive symptoms. Following the Day 1 visit, they will complete a 7 day cell phone EMA component in which they record their current experience of negative life events, rumination, and mood 4 times a day (Days 2-8). Following a one week buffer period to lessen recency effects, the participant will return to the lab to complete an incidental free recall task of all negative life events experienced as well as to complete follow-u trait measures of rumination and depressive symptoms (Day 15). The proposed study will employ powerful statistical tests in order to identify patterns in which depressive symptoms develop in relation to rumination, either in direct response to stress or in the absence of proximal stress. Conclusions derived from this state-level data aim to inform more tailored treatments and interventions that target specific cognitive patterns that may confer risk for the development of depressive symptoms.